This application claims priority of Korea patent Application No. 2000-82948, filed on Dec. 27, 2000, the disclosure of which is incorporated by reference herein.
(a) Field of the Invention
The present invention relates to a malfunction diagnostic method and system for a vehicle speed sensor. More particularly, the present invention relates to a malfunction diagnostic method and system for an output shaft rpm sensor that detects rpm of a transmission output shaft (transfer drive gear).
(b) Description of the Related Art
An electronic control unit (ECU) is typically provided in a vehicle, where it performs engine and transmission control based on vehicle state conditions that are detected by a plurality of sensors such as a vehicle speed sensor. The ECU also monitors operational states of various systems and parts of the vehicle including the sensors, and generates malfunction codes as needed.
One such sensor that is monitored for malfunctions by the ECU is a transmission output shaft rpm sensor (hereinafter referred to as a xe2x80x9cPG-B sensorxe2x80x9d). The operation of the ECU to determine whether the PG-B sensor is malfunctioning will be described with reference to FIG. 1.
The ECU 160 is connected to a vehicle state detector 100, which performs detection of various drive states and operation of elements, and which outputs corresponding signals to the ECU 160. Among the different sensors included in the vehicle state detector 100 are a vehicle speed sensor 110 for detecting vehicle speed, and a PG-B (pulse generator-B) sensor 120 for detecting rpm of a transmission output shaft. The ECU 160 determines the vehicle speed from the signals output by the vehicle speed sensor 110, and performs conversion of output shaft rpm received from the PG-B sensor 120 into vehicle speed (hereinafter referred to as the xe2x80x9cconverted vehicle speedxe2x80x9d) by multiplying the detected output shaft rpm by a predetermined conversion factor.
In the prior art, the PG-B sensor 120 is determined to be malfunctioning if the converted vehicle speed is less than the vehicle speed detected by the vehicle speed sensor 110 by 30% or more. However, the vehicle speed sensor 110 outputs signals of increasingly higher frequencies as the vehicle increases speed, and if noise develops in the signals of the vehicle speed sensor 110, the ECU 160 determines that the vehicle is travelling at a speed greater than its actual speed. In this case, the converted vehicle speed may be determined to be less than the vehicle speed detected by the vehicle speed sensor 110 by 30% or more when, in fact, it is well over 70% of the vehicle speed output by the vehicle speed sensor 110.
Typically, the ECU 120 provides a limp-home mode, in which limited operation of the vehicle is possible when a sensor used for engine/transmission control malfunctions. That is, the transmission is generally maintained in a predetermined shift speed in the limp-home mode. Accordingly, if the PG-B sensor 120 is erroneously determined to be malfunctioning as described above, the ECU 120 performs control into the limp-home mode, causing a great inconvenience to the driver.
The present invention has been made in an effort to solve the above problems.
It is an object of the present invention to provide a method and system that more precisely determines whether there is a malfunction in an rpm sensor that detects rpm of a transmission output shaft, and which performs shifting into a suitable shift speed in the case where the rpm sensor is determined to be malfunctioning.
To achieve the above object, the present invention provides a malfunction method and system for an output shaft rpm sensor of a transmission. The malfunction diagnostic method comprises the steps of: detecting output shaft rpm of a transmission by the output shaft rpm sensor, and detecting vehicle speed by a vehicle speed sensor; determining whether malfunction conditions, which indicate a malfunction in the output shaft rpm sensor, are satisfied based on the output shaft rpm and the vehicle speed; performing stand-by for a predetermined stand-by time if the malfunction conditions are satisfied; determining whether there is a malfunction in the output shaft rpm sensor using the detected output shaft rpm; and generating malfunction codes if it is determined that there is a malfunction in the output shaft rpm sensor.
The malfunction diagnostic system for an output shaft rpm sensor of a transmission comprises: a vehicle state detector for performing detection of various drive states and operations of elements of a vehicle, and outputting corresponding signals; and an ECU for generating malfunction codes according to the signals output by the vehicle state detector, wherein the vehicle state detector includes a vehicle speed sensor for detecting vehicle speed, and wherein the ECU receives signals of the vehicle speed from the vehicle speed sensor and signals of the output shaft rpm from the output shaft rpm sensor, and determines from the vehicle speed and the output shaft rpm whether malfunction conditions are satisfied. In the case where the malfunction conditions are satisfied and after a predetermined stand-by time has elapsed, the ECU determines whether there is a malfunction in the output shaft rpm sensor using the detected output shaft rpm, after which it generates malfunction codes if the output shaft rpm sensor is malfunctioning.
According to a feature of the present invention, the malfunction conditions are satisfied if the output shaft rpm is greater than or equal to a predetermined rpm, and a rate of reduction in the output shaft rpm is greater than or equal to a predetermined rate of rpm reduction.
According to another feature of the present invention, in the case where the output shaft rpm is greater than or equal to the predetermined rpm and the rate of reduction in the output shaft rpm is less than the predetermined rate of rpm reduction, the malfunction conditions are satisfied if the vehicle speed is greater than a predetermined vehicle speed, if a rate of acceleration of the vehicle speed is less than a predetermined acceleration, and if a converted vehicle speed, which is obtained by converting the output shaft rpm, is less than a predetermined ratio of the vehicle speed.
According to yet another feature of the present invention, the method further comprises the step of detecting a shift speed of the transmission, and the vehicle state detector further includes a shift speed sensor for detecting the shift speed of the transmission, and wherein determining whether the malfunction conditions are satisfied is performed if the shift speed is at a predetermined shift speed(s).
According to still yet another feature of the present invention, it is determined that there is a malfunction in the output shaft rpm sensor if, after the predetermined stand-by time has elapsed, a predetermined condition is satisfied for a duration of a predetermined hold time.
According to still yet another feature of the present invention, the method further comprises the step of detecting turbine rpm, and the vehicle state detector further includes a turbine rpm sensor for detecting rpm of a turbine of a torque converter, and wherein, in the case where the detected vehicle speed is greater than or equal to a predetermined vehicle speed or the turbine rpm is greater than or equal to a predetermined turbine rpm, the predetermined condition is satisfied if the output shaft rpm is less than or equal to a second predetermined rpm.
According to still yet another feature of the present invention, the method further comprises the steps of, and the ECU performs the additional operations of: detecting a frequency of the number of times the malfunction codes are generated; determining if the frequency is greater than or equal to a predetermined frequency; and maintaining the transmission in a predetermined shift speed by outputting shift control signals if the frequency is greater than or equal to the predetermined frequency.
According to still yet another feature of the present invention, the method further comprises the step of detecting a positioning of a shift lever, and the vehicle state detector further includes a shift lever position sensor for detecting a positioning of a shift lever, wherein the predetermined shift speed is a second speed in the case where the shift lever is positioned in a low L range or a low 2 range, and is a third speed in the case where the shift lever is in any other forward range.